The present invention is directed to integrated circuits. More particularly, the invention provides systems and methods for enhancing dynamic responses. Merely by way of example, the invention has been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability.
A switching power conversion system often needs not only a good dynamic response under different load conditions, but also good stability. FIG. 1 is a simplified diagram showing a conventional switching power conversion system with a step-down structure. The switching power conversion system 100 includes a system controller 102, a switch 104, a capacitor 106, two diodes 108 and 110, and an inductor 112. For example, an output voltage 120 of the power conversion system 100 usually needs to be regulated to be approximately constant, and relatively stable if output load varies.
FIG. 2 is a simplified conventional diagram showing certain components of the system controller 102 as part of the power conversion system 100. The system controller 102 includes an error amplifier 202, a control component 204, and a gate driver 206. In addition, the system controller 102 uses a compensation network 208 that includes capacitors 210 and 212 and a resistor 214.
The error amplifier 202 receives a feedback signal 216 that is related to the output voltage 120 and a reference signal 218 and generates an amplified signal 220 which indicates load conditions of the system 100. The control component 204 receives the amplified signal 220 and outputs a modulation signal 222 to the gate driver 206 which generates a gate drive signal 224 to drive the switch 104. The compensation network 208 is connected to an output terminal of the error amplifier 202. If the amplified signal 220 is large in magnitude which indicates that the average output voltage 120 is far different from the reference signal 218, the control component 204 adjusts the modulation signal 222 to increase the switching frequency and duty cycles so that more power can be delivered to the output load.
A bandwidth of the control loop often needs to be very small in order to regulate the output voltage 120 to be approximately constant. The dominant pole of the control loop is associated with the error amplifier 202 and the compensation network 208. Usually, the capacitor 212 has a large capacitance in order to reduce the bandwidth of the control loop. But, the large capacitance of the capacitor 212 negatively affects the dynamic response of the power conversion system 100 if the load conditions change.
To achieve a good dynamic response, a wide bandwidth of the control loop for the power conversion system 100 is often needed. For example, the compensation network 208 can be removed to increase the bandwidth of the control loop. Then, the error amplifier 202 becomes a comparator, and the output of the error amplifier 202 changes from rail to rail which results in significant changes in switching frequency and duty cycles. The power conversion system 100 thus operates in an on-off mode (e.g., an ON/OFF mode), instead of an error amplifier mode (EA mode). The wide bandwidth of the control loop, however, often negatively affects the stability of the power conversion system 100, even if the output load is steady. A complex compensation network with a large number of external components is usually needed to obtain both good dynamic response and satisfactory stability. But such a compensation network often significantly increases the system cost.
Hence it is highly desirable to improve the techniques of enhancing dynamic responses of power conversion systems.